Torque-limiting coupling device

ABSTRACT

A torque-limiting clutch arrangement which comprises a cylindrical part (3) forming part of one clutch element and having shrink-fitted thereon a cylindrical sleeve (5) which forms part of the other clutch element. The clutch arrangement also includes a pump which when one clutch element (3) rotates relative to the other clutch element (5), when the torque on the clutch exceeds a given value, functions to pump oil into the domain of engagement between the cylindrical part (3) and the sleeve (5), so as to form a hydrostatic layer therebetween, the hydrostatic layer essentially negating the friction between the engagement surfaces while the relative movement continues.

The present invention relates to a torque-limiting clutch arrangementwhich comprises two mutually coaxial clutch elements which arenon-rotatably connected to a driving shaft and a driven shaftrespectively and which engage one another through the intermediary oftwo mutually opposing, pressurized surfaces, therewith forming afriction joint which is dimensioned to slip when the torque on theclutch exceeds a predetermined value; and a device which is operative todetect slip occurrences in the friction joint and to disengage orseparate the clutch elements when slip occurs.

Torque-limiting clutches or couplings of this kind are known to the artin many different forms. The clutch normally has the form of aconventional disc-clutch comprising a pressure plate which is applied bymeans of a powerful spring force When slip occurs, a device comes intofunction and relieves the pressure on the pressure plate, so as todisengage the clutch. In the case of one simple design, described andillustrated in DE 22 15 053, the spring pressure is generated bycompressed-air springs which are pressurized via a compressed-airconduit. This conduit communicates with an outwardly projecting nipplemounted on one clutch element. The nipple is closed at one end and whenrelative rotation occurs between the two clutch elements, the nipple ispunctured by a moveable member provided on the other of saidclutch-elements.

Such a clutch arrangement is both complicated and space-demanding,particularly when intended for high torques. Another drawback with aclutch of this kind is that once the clutch is overloaded, so that theclutch is disengaged and the driven shaft has stopped, the clutch cannotbe reengaged until the nipple has been replaced and the compressed-airsprings repressurized.

The object of the present invention is to provide a clutch of the kinddescribed in the introduction which is of simple and reliableconstruction and which will remain reliable, even after several years inuse; which is particularly adapted for high torques; and which whendisengaged under overload conditions is ready for re-use immediately,without needing to replace any of the clutch components or to take anyother form of remedial action with respect to the clutch.

SUMMARY OF THE INVENTION

This object is achieved with a clutch constructed in accordance with theinvention and having the characteristic features set forth in thefollowing claims. Considered as a clutch arrangement, the inventivearrangement has the simplest and most-compact construction possible,namely a cylindrical sleeve which is clamped rigidly, preferablyshrink-fitted, onto a cylindrical part. Moveable parts, i.e. pump meansdriven by mutual rotation of the cylindrical parts, do not begin tofunction until slip occurs between the cylindrical parts as a result ofan overload Pressure fluid is delivered to a pressure conduit at therequisite pressure, such as to force the fluid through openings providedin at least one of said friction surfaces and produce a hydrostaticlayer which separates the two cylindrical parts so that the frictiongenerated therebetween will be at a minimum. Immediately upon cessationof the mutual rotation of said parts, the pump means will cease tooperate and the hydrostatic layer is dispersed so as to reestablishfrictional contact between the clutch elements A closed pressure-fluidcircuit is obtained, by providing drainage channels in at least one ofsaid friction surfaces, said circuit enabling the clutch to be helddisengaged over a long period of time, if necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a preferred embodiment of aninventive clutch arrangement, and

FIG. 2 illustrates schematically alterative positioning of the pumpunits of said arrangement.

DETAILED DESCRIPTION

Shown in the drawing is a drive shaft 1 which is keyed by a key 2 to afirst clutch or coupling element comprising a first cylindrical sleeve 3which is press-fitted on one end of the drive shaft and the free-end ofwhich has a first hub 4 firmly mounted thereon. A second or outer sleeve5 having mounted thereon a second hub 6 and belonging to a second clutchelement is shrink-fitted on the outer cylindrical surface of the firstsleeve 3. The second hub 6 has provided therein a central hole in whichthere is firmly mounted a journal pin 7, the end of which facing thedrive shaft 1 is connected to said shaft through the intermediary of aroller bearing 8. The second hub 6 is configured as a flange-connectionfor a driven shaft, e.g. a cardan shaft in an electrically driven unitintended for a track-driven vehicle or the like.

The first hub 4 incorporates six radially extending piston pumps 10,serving as pump unit which are uniformly placed around the hub. Eachpump includes a radial bore 11 which accommodates a piston 12, saidpiston being driven by a strong pressure-spring 13, located between theouter end of the piston and a closure 14. The spring 13 presses theinwardly located end of the piston 12 against an outer-ring 15 of aneedle-bearing, the inner-ring 16 of which is mounted on an excentric 17formed on the journal pin 7. The piston 12 is provided in a conventionalmanner with a suction opening 18, an axial through-flow channel 19, asuction valve 20 mounted in said channel, and a pressure opening 21.

The suction opening 18 communicates with a suction passage 22 whichextends axially through the first hub 4, whereas the pressure opening 21communicates with a pressure passage 23 which also extends through thefirst hub 4. Located opposite the orifice of the pressure passage 23 isan axial outlet channel 24. The channel 24 incorporates a pressure valve25 which coacts with the pump 10, in a known manner.

A radial channel 26 connects the outlet channel 24 with a peripheralgroove 27 in the outer cylindrical wall 28 of the first sleeve 3. Eachof the other five pumps 10 is provided with a peripheral groove, in acorresponding manner. As illustrated in the upper part of FIG. 1, afurther outlet channel 24' is connected to a further peripheral groove27', via a further radial channel 26'. The peripheral grooves 27, 27'are uniformly spaced in the axial direction. Arranged externally of thegroove 27" distal from the first hub 4 is a peripheral drainage groove29 which communicates, via a drainage passage 30, with an annularpressure-fluid storage container 31 located between the clutch elements.The container 31 communicates solely with the suction passages 22 ofrespective piston pumps 10 and with the drainage pasage 30. Two closingdevices 32 and 33, not shown in detail, are provided for the purpose offilling the system with pressure fluid, preferably oil, and ofventilating the closed fluid system.

In normal operation, the inventive clutch arrangement functions as afriction clutch having two clutch sleeves which are joined by ashrink-joint, said joint being adapted so that clutch-slip will onlyoccur when the torque applied to the clutch reaches a predetermined,maximum permitted value.

When this value is reached, the first sleeve 3 and the first hub 4 willrotate relative to the second sleeve 5 and the second hub 6 carrying thejournal pin 7 and the excentric 17. The pistons 12 will then be forcedoutwards in succession and with great force, by the excentricneedle-bearing 15, 16, and then returned by the springs 13. When thepressure-fluid system is filled with oil, oil will consequently bepressed into the peripheral grooves 27, thereby separating the twosleeves 3, 5 sufficiently to enable the oil to leave the grooves 27 andenter the drainage passage 29, from where the oil flows through thedrainage pasage 30 and back to the container 31. There is thus formedbetween the first and second sleeves 3 and 5 a hydrostatic layer whichwill permit the sleeves to rotate mutually with only very littlefriction therebetween.

Slipping between the sleeves 3 and 5 will stop immediately when thetorque acting on the clutch has fallen to a sufficiently low level. Thepumps 10 will then cease to work and the oil in the grooves 27 will loseits pressure. Consequently, the oil is forced away from the interspacebetween the grooves 27, and the two sleeves 3 and 5 are then restored tofrictional engagement as a result of the shrink joint.

The illustrated and described clutch arrangement is intended primarilyfor use with rapid-speed clutches or couplings which operate with onepump-stroke per revolution and pump. In the case of slower clutches itmay be more expedient to use a cam-curve which enables more pump-strokesto be effected per revolution and pump. In this case, the pump units canthen be disposed axially, as shown schematically in FIG. 2. Thisillustration shows separate piston-pumps 40 mounted externally on theouter or second sleeve 5 of the clutch arrangement, and a cam-curve 41mounted rigidly on the shaft 1. Piston rods 42 provided with roller-typecam-followers 42 transmit pumping movement from the camcurve 41 to thepistons of the pumps (not shown) when relative movement occurs betweenthe outer sleeve 5 and the shaft 1. With the exception of the pumps 10and the excentric 17, the clutch shown in FIG. 2 is the same as thatshown in FIG. 1, although in the case of the FIG. 2 embodiment it may beexpedient to form the peripheral grooves 27 with associated passages inthe outer sleeve 5, since the pumps 40 are mounted on said sleeve.

It will be understood that the invention is not restricted to theillustrated and described embodiments and that various modifications canbe made within the scope of the invention defined in the followingclaims, for instance, the piston-pumps 40 of the FIG. 2 embodiment canbe mounted in axial bores in the wall of the outer sleeve 5, in a mannercorresponding to the pumps 10 in the radial bores 11 provided in thefirst hub 4. The number of pumps can, of course, vary in dependence onthe pressure-fluid requirement.

I claim:
 1. A torque-limiting clutch arrangement comprising:two mutuallycoaxial clutch elements which are non-rotatably connected to a drivingshaft and a driven shaft respectively and which engage one anotherthrough the intermediary of two mutually opposing friction-surfacespressed against each other and forming a friction-joint which isdimensioned to slip when a torque on the clutch exceeds a predeterminedvalue; and a detecting device for detecting slip occurrences in thefriction-joint and to disengage the clutch elements when slip occurs;said friction-joint comprising: a cylindrical part (3) which is rigidlyconnected to one of said clutch elements and which has press-fittedthereon a cylindrical sleeve (5) which is connected rigidly to the otherof said clutch elements; a high-pressure pump means (10) which is drivenby the detecting device (17) to supply pressure-fluid to an outletpassage (24) when slip occurs in the friction-joint; and a plurality ofopenings (27) formed in at least one of the friction-surfaces andcommunicating with the outlet pasage (24) of the pump means, saidopenings being configured to produce a hydrostatic layer together withthe friction-surfaces upon the delivery of pressure fluid.
 2. A clutcharrangement according to claim 1 wherein:said pump means (10) is mountedon one of said elements; and said openings (27) connected with theoutlet passage (24) of said one clutch element are formed on thefriction-surface of the same clutch elements (3, 4).
 3. A clutcharrangement according to claim 1 wherein;said pump means includes aplurality of piston-pump housings (11) which extend radially and insubstantially uniform spaced relationship around the one clutch element(3, 43); and said pumps include piston rods (12) having free ends whichare configured for axial activation by an excentric (17) mounted on theother of said clutch elements (5, 6), when one clutch element rotatesrelative to the other clutch element.
 4. A clutch arrangement accordingto claim 2, wherein:said pump means includes a plurality of piston-pumphousings (11) which extend radially and in substantially uniform spacedrelationship around the one clutch element (3, 4); and said pumpsinclude piston rods (12) having free ends which are configured for axialactivation by an excentric (17) mounted on the other of said clutchelements (5, 6), when one clutch element rotates relative to the otherclutch element.
 5. A clutch arrangement according to claim 1, wherein atleast one of said friction-surfaces is provided with grooves (29) whichform drainage passages connected to a suction side (18) of the pumpmeans, to thereby form a closed pressure-fluid circuit.
 6. A clutcharrangement according to claim 2, wherein at least one of saidfriction-surfaces is provided with grooves (29) which form drainagepassages connected to a suction side (18) of the pump means, to therebyform a closed pressure-fluid circuit.
 7. A clutch arrangement accordingto claim 3, wherein at least one of said friction-surfaces is providedwith grooves (29) which form drainage passages connected to a suctionside (18) of the pump means, to thereby form a closed pressure-fluidcircuit.
 8. A clutch arrangement according to claim 1, furthercomprising a plurality of separate pump units (10) arranged on apressure side of the pump means, each pump unit (10) being assigned agiven group of openings (27, 27') which communicate solely with apressure-fluid outlet-passage (24, 24') of an associated pump unit.
 9. Aclutch arrangement according to claim 2, further comprising a pluralityof separate pump units (10) arranged on a pressure side of the pumpmeans, each pump unit (10) being assigned a given group of openings (27,27') which communicate solely with a pressure-fluid outlet-passage (24,24') of an associated pump unit.
 10. A clutch arrangement according toclaim 3, further comprising a plurality of separate pump units (10)arranged on a pressure side of the pump means, each pump unit (10) beingassigned a given group of openings (27, 27') which communicate solelywith a pressure-fluid outlet-passage (24, 24') of an associated pumpunit.
 11. A clutch arrangement according to claim 4, further comprisinga plurality of separate pump units (10) arranged on a pressure side ofthe pump means, each pump unit (10) being assigned a given group ofopenings (27, 27') which communicate solely with a pressure-fluidoutlet-passage (24, 24') of an associated pump unit.